Which bird is this?

Which bird is this?

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Found this today in my neighborhood, my mom says it's a baby vulture and she has seen many during her childhood (in 1970's) while she lived in a small town around 200kms away from our city. However I want to know of it is really vulture cause there are less than 1000 left in whole state and certainly they don't usually fly around here. Even Monkeys (which are, FYI, common in India in small cities and are not afraid by humans) are mad because of this bird's presence but perhaps too frightened to go near him/her. It'd be nice if you guys can tell me what it is :).

I live in Gujarat, India if it helps.

It looks a lot like a African sacred ibis (Threskiornis aethiopicus) (wikilink). However, given your location in India, the closely related Black-headed ibis (which some consider to be part of the same species) might be more likely.

The African sacred ibis is native to mainly sub-saharan Africa, but is considered Invasive in some parts of the world (inkl. Europe and parts of Asia). The Black-headed ibis is however a native breeding bird to large parts of Asia (inkl. India), which makes this more likely.

(Black-headed ibis from wikipedia)

Which bird is this? - Biology

Kentucky Ornithological Society

Bird Identification & Biology

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Interesting Insights from the Booby Bird!

Boobies are birds that have adapted to foraging out at sea and living in large groups. As such, many adaptations exist that have enabled them to do so. These adaptations, and other traits, provide examples of some exciting concepts in biology.

Feeding Adaptations

As seabirds, boobies spend most of their time out at sea and have become experts at foraging for fish in the ocean. Boobies are known for being exceptional divers. They hunt using surprise plunge attacks, diving directly into the ocean from great heights. Boobies are so good at diving that they can dive from as high at 100m above the water and dive 15m below the surface. There are several unique adaptations that these birds have that make this possible.

The first thing that you notice about a booby is that it is very streamlined. It has long, narrow wings and a slender body. When the bird spots its prey, they fold the wings over their body and dive headfirst into the water in a swift vertical drop.

Secondly, if you look at the booby’s bill, you will notice that there are no nostrils. This is because the nose is hidden under the upper mandible to prevent water from being forced into the bird’s trachea when it dives.

Boobies also have internal airbags and a third translucent eyelid. The sacs of air are found under the skin on the bird’s face and chest and provide a cushion that protects the internal organs upon impact with the water. The third eyelid – called the nictitating membrane – provides protection from impact by extending over the eye just before a booby hits the water.

Courtship Rituals

Like many seabirds, boobies are colonial birds. They nest together in groups which can sometimes be very large and crowded. They typically mate with the same partner for several years. Although they live in colonies, boobies can be very territorial. They will protect their area within the large breeding colony through the use of elaborate displays, including head nodding and jabbing.

Courtship also involves displays. The males will perform ritualized dances with many components, including whistling and raising their feet. The birds raise their feet alternately several times, followed by a gesture that ornithologists call sky pointing. Sky pointing involves the birds extending their wings horizontally and raising their heads before emitting a long whistle.

If the female is impressed by the male’s display then mating will follow. Booby birds typically lay between one and three eggs. The incubation period lasts between four and five weeks.

Behavioral Isolation

The elaborate courtship rituals described previously are not only used to attract a mate but are also an example of behavioral isolation.

Also known as ethological isolation, behavioral isolation occurs when two populations are capable of interbreeding but don’t because of differences in their courtship rituals. Courtship rituals involve various signals including audio signals such as breeding calls, visual cues such as mating dances, and olfactory signals such as pheromones. Differences between these signals are what set the species apart.

These differences in their elaborate courtship rituals isolate them from other, closely related species. Lets us consider how this relates to the booby bird. The six species of booby bird overlap and several species can be found sharing the same habitat. The differences in their mating rituals help them to find the correct mating partner and prevent them from mating outside of their species.

By preventing interbreeding, behavioral isolation ensures that the bird does not waste effort in searching, courting, and mating with a partner that will not produce fertile offspring. Producing a fertile offspring is necessary for the continuation of a species, and so behavioral isolation is a fundamental biological mechanism.


This diagram shows the eye structure of a typical raptor :

Birds of prey have very highly developed vision. Possessing more rods and cones than other vertebrates, provides them with advanced visual acuity and their retina is one and a half times thicker. The eyes of a raptor are very big. Taking up 2/3 of the space in their skull, they almost touch each other inside the skull.

Cones : Photoreceptor cells in the retina that perceive colours and permit the formation of precise images.

Rods : Visual receptors in the retina that are very sensitive to low light, they facilitate the detection of movements.

Retina : Photosensitive membrane of the eye where rods and cones are located.

Colour vision and night vision

Diurnal birds of prey can see more colours and can perceive objects about three times farther away than humans can. But their vision at night is weak.

It seems that nocturnal birds of prey cannot distinguish colours. Yet despite what people may think, owls see very well during the day. In fact the Great Horned Owl (Bubo virginianus) sees even better during the day than at night and it sees absolutely nothing in total darkness!

Owls possess a pupil (black circle at the centre of the eye) that they are able to dilate and contract by themselves (unlike humans whose pupils are controlled involuntarily). When an owl dilates its pupil in the darkness, it lets more light enter into the eye. This characteristic, along with the large number of rods in their eyes promotes a nocturnal vision in owls, which is three times better than ours.

Eye protection

Diurnal birds of prey, eagles and hawks particularly, possess a pronounced protruded brow bone that acts like a baseball cap, protecting their eyes from direct sunlight.

Falcons have black or dark moustaches under the eyes that absorb sunlight, thus preventing the glare of the sun from getting into their eyes. Football players use this same idea, which is why they paint black stripes under their eyes.

The nictitating membrane is a third transparent eyelid that sweeps the eye from the inside to the outside of the eye. This eyelid is quite transparent and allows light to pass through, it protects the eye, during flight and hunting they act like security goggles.

Field of vision : The raptor’s field of vision is very wide, and is especially concentrated in the front. Compared to other birds like pigeons, whose eyes are on the sides of the head, the eyes of birds of prey are situated in the front of the head. This provides them with a binocular vision that is well adapted for hunting.

Fixed eyes

The eyes of birds of prey are fixed to the inside of their sockets. Unlike us, they cannot move their eyes to the left and right, without moving their head. To counter this inconvenience, they have a particularly mobile vertebral column, possessing up to14 vertebrae. Humans have only 7 vertebrae. This unique feature is what permits birds of prey to rotate their heads 270 degrees or ¾ of a turn to each side. They cannot do a full turn as many people think.

The shape of a bird’s beak is adapted to its diet. Birds of prey have a hooked beak, curved with very sharp edges. Their beak is not used to catch their prey but to cut through flesh and tear off meat.

The Falcon Tooth

Falcons possess a small projection on each side of their upper beak called a falcon tooth (tomial tooth) and a notch on the lower beak to make room for this “tooth”. Falcons use their teeth to quickly kill their prey, fitting them between the vertebrae and swiftly breaking the neck.

Central Bony Tubercle

How can a falcon breathe when diving at such fast speeds? Its nostrils have a small cone-like, bony central tubercle that deflects air. Slowing down the air entering the nostril, it helps reduce the pressure that could enter into the lungs when the bird is diving at high speeds. Modern jet engines are designed after this falcon feature. There’s a lot to learn from Nature!

The voice and calls of raptors

Birds of prey are not known for their delightful songs, seeing as how they cry or hoot (owls), to communicate. Some have an intense and piercing call, like the Peregrine Falcon (Falco peregrinus) and Red-tailed Hawk (Buteo jamaicensis). While others have funny calls, like the Bald Eagle (Haliaeetus leucocephalus), whose cry sounds like that of a seagull. Vultures, on the other hand, have no vocal cords and can only grunt.


Owls are well known for their hooting. They will usually produce these sounds during the mating season. Males and females will hoot to communicate with one another. Certain owls, like the Great Horned Owl (Bubo virginianus), produce a typical hooting call (hoo hoo), while other species have a variety of different calls. The Eastern Screech Owl’s (Otus asio) call for instance, sounds like the neighing of a horse, and the Barn owl (Tyto alba) produces a scary shriek.

My New Avian Journey

So yesterday, I teased that I would be starting a new bird-related journey soon. Well, without further ado:

I will be taking the Cornell Lab of Ornithology’s Comprehensive course in Bird Biology!

If you’ve been reading my blog for awhile, I’m sure you know that the Cornell Lab of Ornithology is one of my favorite places. It’s one of my main sources of avian information and we even took our 2016 vacation to Ithaca, NY specifically to go birding at the Lab (you can read about that here and here). As a Lab member, I’ve spent countless hours on their website reading articles, watching videos, taking webinars, and watching bird cams.

So when I learned about their Bird Biology class, I knew I had to take it. My dream is to be a Conservation Biologist/Environmental Scientist/Ornithologist, which is why when I’m not at my non-science related full-time job, I’m taking night/summer classes as a biology major. But when I found out about the Lab’s course, I knew it would exactly what I needed to start moving forward with my goals.

The Lab’s Bird Biology course is a university-level self-study course that anyone interesting in birds can take. The course was developed was by one of my favorite ornithologists, Dr. Kevin McGowan, as well as Dr. Sarah Wagner. (Side note: I took a webinar with Kevin McGowan a few winters ago: Odd Ducks and Wandering Waterfowl. If you’re interested in identification courses I recommend checking out his classes/webinars). The course consists of using the textbook (pictured above) and online resources, as well as multiple tests and quizzes for each chapter.

Pretty much anything you would want to know about birds can be found in this course. Topics covered throughout the 700-page book include anatomy, evolution, migration, vocal behavior, social behavior, ecology of populations, and flight to name a few topics. I’m so excited to dive even further into the avian world and share some of the information I learn with you!

If your interesting in learning about the Cornell Lab’s Bird Biology course check out their website.


The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. [26] Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. [27] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda. [28]


Aves and a sister group, the order Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica. [29] However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and is used by many scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils, and assigning them, instead, to the broader group Avialae, [30] in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.

Gauthier and de Queiroz [31] identified four different definitions for the same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. He assigned other names to the other groups.

  1. Aves can mean all archosaurs closer to birds than to crocodiles (alternately Avemetatarsalia)
  2. Aves can mean those advanced archosaurs with feathers (alternately Avifilopluma)
  3. Aves can mean those feathered dinosaurs that fly (alternately Avialae)
  4. Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "crown group", in this sense synonymous with Neornithes)

Under the fourth definition Archaeopteryx, traditionally considered one of the earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. [32]

Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all theropods closer to birds than to Deinonychus", [34] [35] with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus. [36] Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier, who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them. [31] [37]

Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition is synonymous to Avifilopluma. [38]

Dinosaurs and the origin of birds

Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs, [41] and more specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurids and oviraptorosaurs, among others. [42] As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod feathered dinosaurs, contribute to this ambiguity. [43] [44] [45]

The consensus view in contemporary palaeontology is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids. [46] Together, these form a group called Paraves. Some basal members of Deinonychosauria, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both. [47] [48] Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were omnivores. [49]

The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. [50]

Early evolution

Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs, i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex. The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. [33] [52] After the appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer. [33] The integument evolved into complex, pennaceous feathers. [52]

The oldest known paravian (and probably the earliest avialan) fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi, Xiaotingia zhengi, and Aurornis xui. [32]

The well-known probable early avialan, Archaeopteryx, dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial manoeuvreing. [53]

Avialans diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). [54] Increasingly stiff tails (especially the outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle, an ossification of fused tail vertebrae. [33] In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. [55] Around 95 million years ago, they evolved a better sense of smell. [56]

A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula, and the loss of grasping hands. [33]

Early diversity of bird ancestors

The first large, diverse lineage of short-tailed avialans to evolve were the Enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the Mesozoic era. [54]

Many species of the second major avialan lineage to diversify, the Euornithes (meaning "true birds", because they include the ancestors of modern birds), were semi-aquatic and specialised in eating fish and other small aquatic organisms. Unlike the Enantiornithes, which dominated land-based and arboreal habitats, most early euornithes lacked perching adaptations and seem to have included shorebird-like species, waders, and swimming and diving species.

The latter included the superficially gull-like Ichthyornis [58] and the Hesperornithiformes, which became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic. [54] The early euornithes also saw the development of many traits associated with modern birds, like strongly keeled breastbones, toothless, beaked portions of their jaws (though most non-avian euornithes retained teeth in other parts of the jaws). [59] Euornithes also included the first avialans to develop true pygostyle and a fully mobile fan of tail feathers, [60] which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight. [53]

A study on mosaic evolution in the avian skull found that the last common ancestor of all Neornithes might have had a beak similar to that of the modern hook-billed vanga and a skull similar to that of the Eurasian golden oriole. As both species are small aerial and canopy foraging omnivores, a similar ecological niche was inferred for this hypothetical ancestor. [61]

Diversification of modern birds

All modern birds lie within the crown group Aves (alternately Neornithes), which has two subdivisions: the Palaeognathae, which includes the flightless ratites (such as the ostriches) and the weak-flying tinamous, and the extremely diverse Neognathae, containing all other birds. [62] These two subdivisions are often given the rank of superorder, [63] although Livezey and Zusi assigned them "cohort" rank. [28] Depending on the taxonomic viewpoint, the number of known living bird species varies anywhere from 9,800 [64] to 10,758. [65]

The discovery of Vegavis from the Maastrichtian, the last stage of the Late Cretaceous proved that the diversification of modern birds started before the Cenozoic era. [66] The affinities of an earlier fossil, the possible galliform Austinornis lentus, dated to about 85 million years ago, [67] are still too controversial to provide a fossil evidence of modern bird diversification. In 2020, Asteriornis from the Maastrichtian was described, it appears to be a close relative of Galloanserae, the earliest diverging lineage within Neognathae. [68]

Most studies agree on a Cretaceous age for the most recent common ancestor of modern birds but estimates range from the Middle Cretaceous [69] to the latest Late Cretaceous. [70] [1] Similarly, there is no agreement on whether most of the early diversification of modern birds occurred before or after the Cretaceous–Palaeogene extinction event. [71] This disagreement is in part caused by a divergence in the evidence most molecular dating studies suggests a Cretaceous evolutionary radiation, while fossil evidence points to a Cenozoic radiation (the so-called 'rocks' versus 'clocks' controversy). Previous attempts to reconcile molecular and fossil evidence have proved controversial, [71] [72] but more recent estimates, using a more comprehensive sample of fossils and a new way of calibrating molecular clocks, showed that while modern birds originated early in the Late Cretaceous in Western Gondwana, a pulse of diversification in all major groups occurred around the Cretaceous–Palaeogene extinction event. Modern birds expanded from West Gondwana to the Laurasia through two routes. One route was an Antarctic interchange in the Paleogene. This can be confirmed with the presence of multiple avian groups in Australia and New Zealand. The other route was probably through North American, via land bridges during the Paleocene. This allowed the expansion and diversification of Neornithes into the Holarctic and Paleotropics. [73]

Classification of bird orders

Cladogram of modern bird relationships based on Kuhl, H. et al. (2020) [1]

The classification of birds is a contentious issue. Sibley and Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds, [75] although it is frequently debated and constantly revised. Most evidence seems to suggest the assignment of orders is accurate, [76] but scientists disagree about the relationships between the orders themselves evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders. [70] [77]


As of 2020 [update] , the genome has been sequenced for at least one species in about 90% of extant avian families (218 out of 236 families recognised by the Howard and Moore Checklist). [78]

Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the snow petrel's breeding colonies up to 440 kilometres (270 mi) inland in Antarctica. [80] The highest bird diversity occurs in tropical regions. It was earlier thought that this high diversity was the result of higher speciation rates in the tropics however recent studies found higher speciation rates in the high latitudes that were offset by greater extinction rates than in the tropics. [81] Many species migrate annually over great distances and across oceans several families of birds have adapted to life both on the world's oceans and in them, and some seabird species come ashore only to breed, [82] while some penguins have been recorded diving up to 300 metres (980 ft) deep. [83]

Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate the ring-necked pheasant, for example, has been introduced around the world as a game bird. [84] Others have been accidental, such as the establishment of wild monk parakeets in several North American cities after their escape from captivity. [85] Some species, including cattle egret, [86] yellow-headed caracara [87] and galah, [88] have spread naturally far beyond their original ranges as agricultural practices created suitable new habitat.

Compared with other vertebrates, birds have a body plan that shows many unusual adaptations, mostly to facilitate flight.

Skeletal system

The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system. [89] The skull bones in adults are fused and do not show cranial sutures. [90] The orbital cavities that house the eyeballs are large and separated from each other by a bony septum (partition). The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae. [91] The last few are fused with the pelvis to form the synsacrum. [90] The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings. [92] The wings are more or less developed depending on the species the only known groups that lost their wings are the extinct moa and elephant birds. [93]

Excretory system

Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid, instead of urea or ammonia, through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with faeces as a semisolid waste. [94] [95] [96] However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. [97] They also excrete creatine, rather than creatinine like mammals. [90] This material, as well as the output of the intestines, emerges from the bird's cloaca. [98] [99] The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets. [100]

It is a common but not universal feature of altricial passerine nestlings (born helpless, under constant parental care) that instead of excreting directly into the nest, they produce a fecal sac. This is a mucus-covered pouch that allows parents to either dispose of the waste outside the nest or to recycle the waste through their own digestive system. [101]

Reproductive system

Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves. [102] [103] The length is thought to be related to sperm competition. [104] When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. Female birds have sperm storage tubules [105] that allow sperm to remain viable long after copulation, a hundred days in some species. [106] Sperm from multiple males may compete through this mechanism. Most female birds have a single ovary and a single oviduct, both on the left side, [107] but there are exceptions: species in at least 16 different orders of birds have two ovaries. Even these species, however, tend to have a single oviduct. [107] It has been speculated that this might be an adaptation to flight, but males have two testes, and it is also observed that the gonads in both sexes decrease dramatically in size outside the breeding season. [108] [109] Also terrestrial birds generally have a single ovary, as does the platypus, an egg-laying mammal. A more likely explanation is that the egg develops a shell while passing through the oviduct over a period of about a day, so that if two eggs were to develop at the same time, there would be a risk to survival. [107]

Birds are solely gonochoric. [110] Meaning they have two sexes: either female or male. The sex of birds is determined by the Z and W sex chromosomes, rather than by the X and Y chromosomes present in mammals. Male birds have two Z chromosomes (ZZ), and female birds have a W chromosome and a Z chromosome (WZ). [90]

In nearly all species of birds, an individual's sex is determined at fertilisation. However, one recent study claimed to demonstrate temperature-dependent sex determination among the Australian brushturkey, for which higher temperatures during incubation resulted in a higher female-to-male sex ratio. [111] This, however, was later proven to not be the case. These birds do not exhibit temperature-dependent sex determination, but temperature-dependent sex mortality. [112]

Respiratory and circulatory systems

Birds have one of the most complex respiratory systems of all animal groups. [90] Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior air sac which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs. When the bird exhales, the used air flows out of the lungs and the stored fresh air from the posterior air sac is simultaneously forced into the lungs. Thus, a bird's lungs receive a constant supply of fresh air during both inhalation and exhalation. [113] Sound production is achieved using the syrinx, a muscular chamber incorporating multiple tympanic membranes which diverges from the lower end of the trachea [114] the trachea being elongated in some species, increasing the volume of vocalisations and the perception of the bird's size. [115]

In birds, the main arteries taking blood away from the heart originate from the right aortic arch (or pharyngeal arch), unlike in the mammals where the left aortic arch forms this part of the aorta. [90] The postcava receives blood from the limbs via the renal portal system. Unlike in mammals, the circulating red blood cells in birds retain their nucleus. [116]

Heart type and features

The avian circulatory system is driven by a four-chambered, myogenic heart contained in a fibrous pericardial sac. This pericardial sac is filled with a serous fluid for lubrication. [117] The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium.

The sinoatrial node uses calcium to cause a depolarising signal transduction pathway from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The avian heart also consists of muscular arches that are made up of thick bundles of muscular layers. Much like a mammalian heart, the avian heart is composed of endocardial, myocardial and epicardial layers. [117] The atrium walls tend to be thinner than the ventricle walls, due to the intense ventricular contraction used to pump oxygenated blood throughout the body. Avian hearts are generally larger than mammalian hearts when compared to body mass. This adaptation allows more blood to be pumped to meet the high metabolic need associated with flight. [118]


Birds have a very efficient system for diffusing oxygen into the blood birds have a ten times greater surface area to gas exchange volume than mammals. As a result, birds have more blood in their capillaries per unit of volume of lung than a mammal. [118] The arteries are composed of thick elastic muscles to withstand the pressure of the ventricular contractions, and become more rigid as they move away from the heart. Blood moves through the arteries, which undergo vasoconstriction, and into arterioles which act as a transportation system to distribute primarily oxygen as well as nutrients to all tissues of the body. [119] As the arterioles move away from the heart and into individual organs and tissues they are further divided to increase surface area and slow blood flow. Blood travels through the arterioles and moves into the capillaries where gas exchange can occur.

Capillaries are organised into capillary beds in tissues it is here that blood exchanges oxygen for carbon dioxide waste. In the capillary beds, blood flow is slowed to allow maximum diffusion of oxygen into the tissues. Once the blood has become deoxygenated, it travels through venules then veins and back to the heart. Veins, unlike arteries, are thin and rigid as they do not need to withstand extreme pressure. As blood travels through the venules to the veins a funneling occurs called vasodilation bringing blood back to the heart. [119] Once the blood reaches the heart, it moves first into the right atrium, then the right ventricle to be pumped through the lungs for further gas exchange of carbon dioxide waste for oxygen. Oxygenated blood then flows from the lungs through the left atrium to the left ventricle where it is pumped out to the body.

Nervous system

The nervous system is large relative to the bird's size. [90] The most developed part of the brain is the one that controls the flight-related functions, while the cerebellum coordinates movement and the cerebrum controls behaviour patterns, navigation, mating and nest building. Most birds have a poor sense of smell [120] with notable exceptions including kiwis, [121] New World vultures [122] and tubenoses. [123] The avian visual system is usually highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water. [90] Some species also have dual fovea. Birds are tetrachromatic, possessing ultraviolet (UV) sensitive cone cells in the eye as well as green, red and blue ones. [124] They also have double cones, likely to mediate achromatic vision. [125]

Many birds show plumage patterns in ultraviolet that are invisible to the human eye some birds whose sexes appear similar to the naked eye are distinguished by the presence of ultraviolet reflective patches on their feathers. Male blue tits have an ultraviolet reflective crown patch which is displayed in courtship by posturing and raising of their nape feathers. [126] Ultraviolet light is also used in foraging—kestrels have been shown to search for prey by detecting the UV reflective urine trail marks left on the ground by rodents. [127] With the exception of pigeons and a few other species, [128] the eyelids of birds are not used in blinking. Instead the eye is lubricated by the nictitating membrane, a third eyelid that moves horizontally. [129] The nictitating membrane also covers the eye and acts as a contact lens in many aquatic birds. [90] The bird retina has a fan shaped blood supply system called the pecten. [90]

Eyes of most birds are large, not very round and capable of only limited movement in the orbits, [90] typically 10-20°. [130] Birds with eyes on the sides of their heads have a wide visual field, while birds with eyes on the front of their heads, such as owls, have binocular vision and can estimate the depth of field. [130] [131] The avian ear lacks external pinnae but is covered by feathers, although in some birds, such as the Asio, Bubo and Otus owls, these feathers form tufts which resemble ears. The inner ear has a cochlea, but it is not spiral as in mammals. [132]

Defence and intraspecific combat

A few species are able to use chemical defences against predators some Procellariiformes can eject an unpleasant stomach oil against an aggressor, [133] and some species of pitohuis from New Guinea have a powerful neurotoxin in their skin and feathers. [134]

A lack of field observations limit our knowledge, but intraspecific conflicts are known to sometimes result in injury or death. [135] The screamers (Anhimidae), some jacanas (Jacana, Hydrophasianus), the spur-winged goose (Plectropterus), the torrent duck (Merganetta) and nine species of lapwing (Vanellus) use a sharp spur on the wing as a weapon. The steamer ducks (Tachyeres), geese and swans (Anserinae), the solitaire (Pezophaps), sheathbills (Chionis), some guans (Crax) and stone curlews (Burhinus) use a bony knob on the alular metacarpal to punch and hammer opponents. [135] The jacanas Actophilornis and Irediparra have an expanded, blade-like radius. The extinct Xenicibis was unique in having an elongate forelimb and massive hand which likely functioned in combat or defence as a jointed club or flail. Swans, for instance, may strike with the bony spurs and bite when defending eggs or young. [135]

Feathers, plumage, and scales

Feathers are a feature characteristic of birds (though also present in some dinosaurs not currently considered to be true birds). They facilitate flight, provide insulation that aids in thermoregulation, and are used in display, camouflage, and signalling. [90] There are several types of feathers, each serving its own set of purposes. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called pterylae. The distribution pattern of these feather tracts (pterylosis) is used in taxonomy and systematics. The arrangement and appearance of feathers on the body, called plumage, may vary within species by age, social status, [136] and sex. [137]

Plumage is regularly moulted the standard plumage of a bird that has moulted after breeding is known as the "" plumage, or—in the Humphrey–Parkes terminology—"basic" plumage breeding plumages or variations of the basic plumage are known under the Humphrey–Parkes system as "" plumages. [138] Moulting is annual in most species, although some may have two moults a year, and large birds of prey may moult only once every few years. Moulting patterns vary across species. In passerines, flight feathers are replaced one at a time with the innermost being the first. When the fifth of sixth primary is replaced, the outermost begin to drop. After the innermost tertiaries are moulted, the starting from the innermost begin to drop and this proceeds to the outer feathers (centrifugal moult). The greater primary are moulted in synchrony with the primary that they overlap. [139]

A small number of species, such as ducks and geese, lose all of their flight feathers at once, temporarily becoming flightless. [140] As a general rule, the tail feathers are moulted and replaced starting with the innermost pair. [139] Centripetal moults of tail feathers are however seen in the Phasianidae. [141] The centrifugal moult is modified in the tail feathers of woodpeckers and treecreepers, in that it begins with the second innermost pair of feathers and finishes with the central pair of feathers so that the bird maintains a functional climbing tail. [139] [142] The general pattern seen in passerines is that the primaries are replaced outward, secondaries inward, and the tail from centre outward. [143] Before nesting, the females of most bird species gain a bare brood patch by losing feathers close to the belly. The skin there is well supplied with blood vessels and helps the bird in incubation. [144]

Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this. [145] The bill is used to brush away foreign particles and to apply waxy secretions from the uropygial gland these secretions protect the feathers' flexibility and act as an antimicrobial agent, inhibiting the growth of feather-degrading bacteria. [146] This may be supplemented with the secretions of formic acid from ants, which birds receive through a behaviour known as anting, to remove feather parasites. [147]

The scales of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of kingfishers and woodpeckers. The scales of birds are thought to be homologous to those of reptiles and mammals. [148]


Most birds can fly, which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for searching for food and for escaping from predators. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil. [90]

Wing shape and size generally determine a bird's flight style and performance many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are flightless, as were many extinct birds. [149] Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators. [150] Although flightless, penguins use similar musculature and movements to "fly" through the water, as do some flight-capable birds such as auks, shearwaters and dippers. [151]

Most birds are diurnal, but some birds, such as many species of owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night. [152]

Diet and feeding

are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds. [90] The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth. [153] Some species such as pigeons and some psittacine species do not have a gallbladder. [154] Most birds are highly adapted for rapid digestion to aid with flight. [155] Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration. [156]

Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists. [90] Avian foraging strategies can vary widely by species. Many birds glean for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek pest insects are considered beneficial 'biological control agents' and their presence encouraged in biological pest control programmes. [157] Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually. [158]

Nectar feeders such as hummingbirds, sunbirds, lories, and lorikeets amongst others have specially adapted brushy tongues and in many cases bills designed to fit co-adapted flowers. [159] Kiwis and shorebirds with long bills probe for invertebrates shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches. [90] [160] Loons, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion, [82] while aerial predators such as sulids, kingfishers and terns plunge dive after their prey. Flamingos, three species of prion, and some ducks are filter feeders. [161] [162] Geese and dabbling ducks are primarily grazers.

Some species, including frigatebirds, gulls, [163] and skuas, [164] engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet a study of great frigatebirds stealing from masked boobies estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%. [165] Other birds are scavengers some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists. [166]

Water and drinking

Water is needed by many birds although their mode of excretion and lack of sweat glands reduces the physiological demands. [167] Some desert birds can obtain their water needs entirely from moisture in their food. They may also have other adaptations such as allowing their body temperature to rise, saving on moisture loss from evaporative cooling or panting. [168] Seabirds can drink seawater and have salt glands inside the head that eliminate excess salt out of the nostrils. [169]

Most birds scoop water in their beaks and raise their head to let water run down the throat. Some species, especially of arid zones, belonging to the pigeon, finch, mousebird, button-quail and bustard families are capable of sucking up water without the need to tilt back their heads. [170] Some desert birds depend on water sources and sandgrouse are particularly well known for their daily congregations at waterholes. Nesting sandgrouse and many plovers carry water to their young by wetting their belly feathers. [171] Some birds carry water for chicks at the nest in their crop or regurgitate it along with food. The pigeon family, flamingos and penguins have adaptations to produce a nutritive fluid called crop milk that they provide to their chicks. [172]

Feather care

Feathers, being critical to the survival of a bird, require maintenance. Apart from physical wear and tear, feathers face the onslaught of fungi, ectoparasitic feather mites and bird lice. [173] The physical condition of feathers are maintained by often with the application of secretions from the . Birds also bathe in water or dust themselves. While some birds dip into shallow water, more aerial species may make aerial dips into water and arboreal species often make use of dew or rain that collect on leaves. Birds of arid regions make use of loose soil to dust-bathe. A behaviour termed as anting in which the bird encourages ants to run through their plumage is also thought to help them reduce the ectoparasite load in feathers. Many species will spread out their wings and expose them to direct sunlight and this too is thought to help in reducing fungal and ectoparasitic activity that may lead to feather damage. [174] [175]


Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, shorebirds, and waterbirds undertake annual long-distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the temperate or polar regions and a non-breeding season in the tropical regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs. [176] [177]

Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around 2,500 km (1,600 mi) and shorebirds can fly up to 4,000 km (2,500 mi), [90] although the bar-tailed godwit is capable of non-stop flights of up to 10,200 km (6,300 mi). [178] Seabirds also undertake long migrations, the longest annual migration being those of sooty shearwaters, which nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of 64,000 km (39,800 mi). [179] Other seabirds disperse after breeding, travelling widely but having no set migration route. Albatrosses nesting in the Southern Ocean often undertake circumpolar trips between breeding seasons. [180]

Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. Irruptive species such as the boreal finches are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability. [181] Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates. [182] Partial migration can form a large percentage of the migration behaviour of birds in some regions in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory. [183]

Altitudinal migration is a form of short-distance migration in which birds spend the breeding season at higher altitudes and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when the normal territories also become inhospitable due to lack of food. [184] Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. Parrots as a family are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations. [185]

The ability of birds to return to precise locations across vast distances has been known for some time in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of 5,150 km (3,200 mi). [186] Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock. [90] Orientation with the stellar compass depends on the position of the constellations surrounding Polaris. [187] These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors. [188]


Birds communicate using primarily visual and auditory signals. Signals can be interspecific (between species) and intraspecific (within species).

Birds sometimes use plumage to assess and assert social dominance, [189] to display breeding condition in sexually selected species, or to make threatening displays, as in the sunbittern's mimicry of a large predator to ward off hawks and protect young chicks. [190] Variation in plumage also allows for the identification of birds, particularly between species.

Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds. [90] The most elaborate displays occur during courtship, where "dances" are often formed from complex combinations of many possible component movements [191] males' breeding success may depend on the quality of such displays. [192]

Bird calls and songs, which are produced in the syrinx, are the major means by which birds communicate with sound. This communication can be very complex some species can operate the two sides of the syrinx independently, allowing the simultaneous production of two different songs. [114] Calls are used for a variety of purposes, including mate attraction, [90] evaluation of potential mates, [193] bond formation, the claiming and maintenance of territories, [90] the identification of other individuals (such as when parents look for chicks in colonies or when mates reunite at the start of breeding season), [194] and the warning of other birds of potential predators, sometimes with specific information about the nature of the threat. [195] Some birds also use mechanical sounds for auditory communication. The Coenocorypha snipes of New Zealand drive air through their feathers, [196] woodpeckers drum for long-distance communication, [197] and palm cockatoos use tools to drum. [198]

Flocking and other associations

While some birds are essentially territorial or live in small family groups, other birds may form large flocks. The principal benefits of flocking are safety in numbers and increased foraging efficiency. [90] Defence against predators is particularly important in closed habitats like forests, where ambush predation is common and multiple eyes can provide a valuable early warning system. This has led to the development of many mixed-species feeding flocks, which are usually composed of small numbers of many species these flocks provide safety in numbers but increase potential competition for resources. [200] Costs of flocking include bullying of socially subordinate birds by more dominant birds and the reduction of feeding efficiency in certain cases. [201]

Birds sometimes also form associations with non-avian species. Plunge-diving seabirds associate with dolphins and tuna, which push shoaling fish towards the surface. [202] Hornbills have a mutualistic relationship with dwarf mongooses, in which they forage together and warn each other of nearby birds of prey and other predators. [203]

Resting and roosting

The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening "peeks", allowing them to be sensitive to disturbances and enable rapid escape from threats. [204] Swifts are believed to be able to sleep in flight and radar observations suggest that they orient themselves to face the wind in their roosting flight. [205] It has been suggested that there may be certain kinds of sleep which are possible even when in flight. [206]

Some birds have also demonstrated the capacity to fall into slow-wave sleep one hemisphere of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for predators by viewing the outer margins of the flock. This adaptation is also known from marine mammals. [207] Communal roosting is common because it lowers the loss of body heat and decreases the risks associated with predators. [208] Roosting sites are often chosen with regard to thermoregulation and safety. [209]

Many sleeping birds bend their heads over their backs and tuck their bills in their back feathers, although others place their beaks among their breast feathers. Many birds rest on one leg, while some may pull up their legs into their feathers, especially in cold weather. Perching birds have a tendon-locking mechanism that helps them hold on to the perch when they are asleep. Many ground birds, such as quails and pheasants, roost in trees. A few parrots of the genus Loriculus roost hanging upside down. [210] Some hummingbirds go into a nightly state of torpor accompanied with a reduction of their metabolic rates. [211] This physiological adaptation shows in nearly a hundred other species, including owlet-nightjars, nightjars, and woodswallows. One species, the common poorwill, even enters a state of hibernation. [212] Birds do not have sweat glands, but they may cool themselves by moving to shade, standing in water, panting, increasing their surface area, fluttering their throat or by using special behaviours like urohidrosis to cool themselves.


Social systems

Ninety-five per cent of bird species are socially monogamous. These species pair for at least the length of the breeding season or—in some cases—for several years or until the death of one mate. [214] Monogamy allows for both paternal care and biparental care, which is especially important for species in which females require males' assistance for successful brood-rearing. [215] Among many socially monogamous species, extra-pair copulation (infidelity) is common. [216] Such behaviour typically occurs between dominant males and females paired with subordinate males, but may also be the result of forced copulation in ducks and other anatids. [217]

For females, possible benefits of extra-pair copulation include getting better genes for her offspring and insuring against the possibility of infertility in her mate. [218] Males of species that engage in extra-pair copulations will closely guard their mates to ensure the parentage of the offspring that they raise. [219]

Other mating systems, including polygyny, polyandry, polygamy, polygynandry, and promiscuity, also occur. [90] Polygamous breeding systems arise when females are able to raise broods without the help of males. [90] Some species may use more than one system depending on the circumstances.

Breeding usually involves some form of courtship display, typically performed by the male. [220] Most displays are rather simple and involve some type of song. Some displays, however, are quite elaborate. Depending on the species, these may include wing or tail drumming, dancing, aerial flights, or communal lekking. Females are generally the ones that drive partner selection, [221] although in the polyandrous phalaropes, this is reversed: plainer males choose brightly coloured females. [222] Courtship feeding, billing and are commonly performed between partners, generally after the birds have paired and mated. [223]

Homosexual behaviour has been observed in males or females in numerous species of birds, including copulation, pair-bonding, and joint parenting of chicks. [224] Over 130 avian species around the world engage in sexual interactions between the same sex or homosexual behaviours. "Same-sex courtship activities may involve elaborate displays, synchronized dances, gift-giving ceremonies, or behaviors at specific display areas including bowers, arenas, or leks." [225]

Territories, nesting and incubation

Many birds actively defend a territory from others of the same species during the breeding season maintenance of territories protects the food source for their chicks. Species that are unable to defend feeding territories, such as seabirds and swifts, often breed in colonies instead this is thought to offer protection from predators. Colonial breeders defend small nesting sites, and competition between and within species for nesting sites can be intense. [226]

All birds lay amniotic eggs with hard shells made mostly of calcium carbonate. [90] Hole and burrow nesting species tend to lay white or pale eggs, while open nesters lay camouflaged eggs. There are many exceptions to this pattern, however the ground-nesting nightjars have pale eggs, and camouflage is instead provided by their plumage. Species that are victims of brood parasites have varying egg colours to improve the chances of spotting a parasite's egg, which forces female parasites to match their eggs to those of their hosts. [227]

Bird eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows. [228] Some bird nests, however, are extremely primitive albatross nests are no more than a scrape on the ground. Most birds build nests in sheltered, hidden areas to avoid predation, but large or colonial birds—which are more capable of defence—may build more open nests. During nest construction, some species seek out plant matter from plants with parasite-reducing toxins to improve chick survival, [229] and feathers are often used for nest insulation. [228] Some bird species have no nests the cliff-nesting common guillemot lays its eggs on bare rock, and male emperor penguins keep eggs between their body and feet. The absence of nests is especially prevalent in ground-nesting species where the newly hatched young are precocial.

Incubation, which optimises temperature for chick development, usually begins after the last egg has been laid. [90] In monogamous species incubation duties are often shared, whereas in polygamous species one parent is wholly responsible for incubation. Warmth from parents passes to the eggs through brood patches, areas of bare skin on the abdomen or breast of the incubating birds. Incubation can be an energetically demanding process adult albatrosses, for instance, lose as much as 83 grams (2.9 oz) of body weight per day of incubation. [230] The warmth for the incubation of the eggs of megapodes comes from the sun, decaying vegetation or volcanic sources. [231] Incubation periods range from 10 days (in woodpeckers, cuckoos and passerine birds) to over 80 days (in albatrosses and kiwis). [90]

The diversity of characteristics of birds is great, sometimes even in closely related species. Several avian characteristics are compared in the table below. [232] [233]

Species Adult weight
(per year)
Clutch size
Ruby-throated hummingbird (Archilochus colubris) 3 13 2.0 2
House sparrow (Passer domesticus) 25 11 4.5 5
Greater roadrunner (Geococcyx californianus) 376 20 1.5 4
Turkey vulture (Cathartes aura) 2,200 39 1.0 2
Laysan albatross (Diomedea immutabilis) 3,150 64 1.0 1
Magellanic penguin (Spheniscus magellanicus) 4,000 40 1.0 1
Golden eagle (Aquila chrysaetos) 4,800 40 1.0 2
Wild turkey (Meleagris gallopavo) 6,050 28 1.0 11

Parental care and fledging

At the time of their hatching, chicks range in development from helpless to independent, depending on their species. Helpless chicks are termed altricial, and tend to be born small, blind, immobile and naked chicks that are mobile and feathered upon hatching are termed precocial. Altricial chicks need help thermoregulating and must be brooded for longer than precocial chicks. The young of many bird species do not precisely fit into either the precocial or altricial category, having some aspects of each and thus fall somewhere on an "altricial-precocial spectrum". [234] Chicks at neither extreme but favouring one or the other may be termed [235] or . [236]

The length and nature of parental care varies widely amongst different orders and species. At one extreme, parental care in megapodes ends at hatching the newly hatched chick digs itself out of the nest mound without parental assistance and can fend for itself immediately. [237] At the other extreme, many seabirds have extended periods of parental care, the longest being that of the great frigatebird, whose chicks take up to six months to fledge and are fed by the parents for up to an additional 14 months. [238] The chick guard stage describes the period of breeding during which one of the adult birds is permanently present at the nest after chicks have hatched. The main purpose of the guard stage is to aid offspring to thermoregulate and protect them from predation. [239]

In some species, both parents care for nestlings and fledglings in others, such care is the responsibility of only one sex. In some species, other members of the same species—usually close relatives of the breeding pair, such as offspring from previous broods—will help with the raising of the young. [240] Such alloparenting is particularly common among the Corvida, which includes such birds as the true crows, Australian magpie and fairy-wrens, [241] but has been observed in species as different as the rifleman and red kite. Among most groups of animals, male parental care is rare. In birds, however, it is quite common—more so than in any other vertebrate class. [90] Although territory and nest site defence, incubation, and chick feeding are often shared tasks, there is sometimes a division of labour in which one mate undertakes all or most of a particular duty. [242]

The point at which chicks fledge varies dramatically. The chicks of the Synthliboramphus murrelets, like the ancient murrelet, leave the nest the night after they hatch, following their parents out to sea, where they are raised away from terrestrial predators. [243] Some other species, such as ducks, move their chicks away from the nest at an early age. In most species, chicks leave the nest just before, or soon after, they are able to fly. The amount of parental care after fledging varies albatross chicks leave the nest on their own and receive no further help, while other species continue some supplementary feeding after fledging. [244] Chicks may also follow their parents during their first migration. [245]

Brood parasites

Brood parasitism, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism. [246] After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either obligate brood parasites, which must lay their eggs in the nests of other species because they are incapable of raising their own young, or non-obligate brood parasites, which sometimes lay eggs in the nests of conspecifics to increase their reproductive output even though they could have raised their own young. [247] One hundred bird species, including honeyguides, icterids, and ducks, are obligate parasites, though the most famous are the cuckoos. [246] Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks this ensures that all food brought to the nest will be fed to the parasitic chicks. [248]

Sexual selection

Birds have evolved a variety of mating behaviours, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and colour differences are energetically costly attributes that signal competitive breeding situations. [249] Many types of avian sexual selection have been identified intersexual selection, also known as female choice and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signalling adaptations ensure that sexually selected ornaments such as plumage colouration and courtship behaviour are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviours. [250]

Inbreeding depression

Inbreeding causes early death (inbreeding depression) in the zebra finch Taeniopygia guttata. [251] Embryo survival (that is, hatching success of fertile eggs) was significantly lower for sib-sib mating pairs than for unrelated pairs.

Darwin's finch Geospiza scandens experiences inbreeding depression (reduced survival of offspring) and the magnitude of this effect is influenced by environmental conditions such as low food availability. [252]

Inbreeding avoidance

Incestuous matings by the purple-crowned fairy wren Malurus coronatus result in severe fitness costs due to inbreeding depression (greater than 30% reduction in hatchability of eggs). [253] Females paired with related males may undertake extra pair matings (see Promiscuity#Other animals for 90% frequency in avian species) that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 43% of broods produced by incestuously paired females contained extra pair young. [253]

Inbreeding depression occurs in the great tit (Parus major) when the offspring produced as a result of a mating between close relatives show reduced fitness. In natural populations of Parus major, inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative. [254]

Southern pied babblers Turdoides bicolor appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates. [255] Although both males and females disperse locally, they move outside the range where genetically related individuals are likely to be encountered. Within their group, individuals only acquire breeding positions when the opposite-sex breeder is unrelated.

Cooperative breeding in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin. [256] Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups. In general, inbreeding is avoided because it leads to a reduction in progeny fitness (inbreeding depression) due largely to the homozygous expression of deleterious recessive alleles. [257] Cross-fertilisation between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny. [258] [259]

Birds occupy a wide range of ecological positions. [199] While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the niches occupied by different species of birds vary, with some species feeding in the forest canopy, others beneath the canopy, and still others on the forest floor. Forest birds may be insectivores, frugivores, and nectarivores. Aquatic birds generally feed by fishing, plant eating, and piracy or kleptoparasitism. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised scavengers. Avivores are animals that are specialised at preying on birds.

Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal. [260] Plants and pollinating birds often coevolve, [261] and in some cases a flower's primary pollinator is the only species capable of reaching its nectar. [262]

Birds are often important to island ecology. Birds have frequently reached islands that mammals have not on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of moa were important browsers, as are the kererū and kokako today. [260] Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa. [263] Nesting seabirds may also affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of guano, which may enrich the local soil [264] and the surrounding seas. [265]

A wide variety of avian ecology field methods, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.

Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man. [266] Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among honeyguides and African peoples such as the Borana. [267] Other times, they may be commensal, as when species such as the house sparrow [268] have benefited from human activities. Several bird species have become commercially significant agricultural pests, [269] and some pose an aviation hazard. [270] Human activities can also be detrimental, and have threatened numerous bird species with extinction (hunting, avian lead poisoning, pesticides, roadkill, wind turbine kills [271] and predation by pet cats and dogs are common causes of death for birds). [272]

Birds can act as vectors for spreading diseases such as psittacosis, salmonellosis, campylobacteriosis, mycobacteriosis (avian tuberculosis), avian influenza (bird flu), giardiasis, and cryptosporidiosis over long distances. Some of these are zoonotic diseases that can also be transmitted to humans. [273]

Economic importance

Domesticated birds raised for meat and eggs, called poultry, are the largest source of animal protein eaten by humans in 2003, 76 million tons of poultry and 61 million tons of eggs were produced worldwide. [274] Chickens account for much of human poultry consumption, though domesticated turkeys, ducks, and geese are also relatively common. Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl other widely hunted birds include pheasants, wild turkeys, quail, doves, partridge, grouse, snipe, and woodcock. [275] Muttonbirding is also popular in Australia and New Zealand. [276] Although some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species. [277]

Other commercially valuable products from birds include feathers (especially the down of geese and ducks), which are used as insulation in clothing and bedding, and seabird faeces (guano), which is a valuable source of phosphorus and nitrogen. The War of the Pacific, sometimes called the Guano War, was fought in part over the control of guano deposits. [278]

Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as parrots and mynas, are bred in captivity or kept as pets, a practice that has led to the illegal trafficking of some endangered species. [279] Falcons and cormorants have long been used for hunting and fishing, respectively. Messenger pigeons, used since at least 1 AD, remained important as recently as World War II. Today, such activities are more common either as hobbies, for entertainment and tourism, [280] or for sports such as pigeon racing.

Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly, birders) number in the millions. [281] Many homeowners erect bird feeders near their homes to attract various species. Bird feeding has grown into a multimillion-dollar industry for example, an estimated 75% of households in Britain provide food for birds at some point during the winter. [282]

In religion and mythology

Birds play prominent and diverse roles in religion and mythology. In religion, birds may serve as either messengers or priests and leaders for a deity, such as in the Cult of Makemake, in which the Tangata manu of Easter Island served as chiefs [283] or as attendants, as in the case of Hugin and Munin, the two common ravens who whispered news into the ears of the Norse god Odin. In several civilisations of ancient Italy, particularly Etruscan and Roman religion, priests were involved in augury, or interpreting the words of birds while the "auspex" (from which the word "auspicious" is derived) watched their activities to foretell events. [284]

They may also serve as religious symbols, as when Jonah (Hebrew: יוֹנָה ‎, dove) embodied the fright, passivity, mourning, and beauty traditionally associated with doves. [285] Birds have themselves been deified, as in the case of the common peacock, which is perceived as Mother Earth by the people of southern India. [286] In the ancient world, doves were used as symbols of the Mesopotamian goddess Inanna (later known as Ishtar), [287] [288] the Canaanite mother goddess Asherah, [287] [288] [289] and the Greek goddess Aphrodite. [287] [288] [290] [291] [292] In ancient Greece, Athena, the goddess of wisdom and patron deity of the city of Athens, had a little owl as her symbol. [293] [294] [295] In religious images preserved from the Inca and Tiwanaku empires, birds are depicted in the process of transgressing boundaries between earthly and underground spiritual realms. [296] Indigenous peoples of the central Andes maintain legends of birds passing to and from metaphysical worlds. [296]

In culture and folklore

Birds have featured in culture and art since prehistoric times, when they were represented in early cave paintings. [297] Some birds have been perceived as monsters, including the mythological Roc and the Māori's legendary Pouākai, a giant bird capable of snatching humans. [298] Birds were later used as symbols of power, as in the magnificent Peacock Throne of the Mughal and Persian emperors. [299] With the advent of scientific interest in birds, many paintings of birds were commissioned for books.

Among the most famous of these bird artists was John James Audubon, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the National Audubon Society. [300] Birds are also important figures in poetry for example, Homer incorporated nightingales into his Odyssey, and Catullus used a sparrow as an erotic symbol in his Catullus 2. [301] The relationship between an albatross and a sailor is the central theme of Samuel Taylor Coleridge's The Rime of the Ancient Mariner, which led to the use of the term as a metaphor for a 'burden'. [302] Other English metaphors derive from birds vulture funds and vulture investors, for instance, take their name from the scavenging vulture. [303]

Perceptions of bird species vary across cultures. Owls are associated with bad luck, witchcraft, and death in parts of Africa, [304] but are regarded as wise across much of Europe. [305] Hoopoes were considered sacred in Ancient Egypt and symbols of virtue in Persia, but were thought of as thieves across much of Europe and harbingers of war in Scandinavia. [306] In heraldry, birds, especially eagles, often appear in coats of arms. [307]

In music

In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong they can intentionally imitate bird song in a composition, as Vivaldi, Messiaen, and Beethoven did, along with many later composers they can incorporate recordings of birds into their works, as Ottorino Respighi first did or like Beatrice Harrison and David Rothenberg, they can duet with birds. [308] [309] [310] [311]


Although human activities have allowed the expansion of a few species, such as the barn swallow and European starling, they have caused population decreases or extinction in many other species. Over a hundred bird species have gone extinct in historical times, [312] although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of Melanesian, Polynesian, and Micronesian islands. [313] Many bird populations are declining worldwide, with 1,227 species listed as threatened by BirdLife International and the IUCN in 2009. [314] [315]

The most commonly cited human threat to birds is habitat loss. [316] Other threats include overhunting, accidental mortality due to collisions with buildings or vehicles, long-line fishing bycatch, [317] pollution (including oil spills and pesticide use), [318] competition and predation from nonnative invasive species, [319] and climate change.

Governments and conservation groups work to protect birds, either by passing laws that preserve and restore bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the California condor and Norfolk parakeet. [320]

North American Breeding Bird Survey

The North American Breeding Bird Survey (BBS) is the primary source for critical quantitative data to evaluate the status of continental bird species, keeping common birds common and helping fuel a $75 billion wildlife watching industry. Each year thousands of citizen scientists skilled in avian identification collect data on BBS routes throughout North America allowing us to better understand bird population changes and manage them. The USGS Patuxent Wildlife Research Center, Environment and Climate Change Canada, and the Mexican National Commission for the Knowledge and Use of Biodiversity jointly coordinate the program, which provides reliable population data and trend analyses on more than 500 bird species.

Participate in the Survey - Each spring over 2500 skilled amateur birders and professional biologists volunteer to participate in the North American BBS. We are always looking for highly skilled birders to join the team.

Get Raw Data - Search and download raw data results

Strategic Plan for the North American Breeding Bird Survey, 2020–30 - The North American Breeding Bird Survey (BBS) has been the cornerstone of continental bird conservation and management for hundreds of North American bird species in the United States and Canada for more than 50 years. This strategic plan was developed in collaboration with key partners and stakeholders and charts the ambitious course for the BBS over the next decade (2020–30). Using this plan as a guide, the BBS program will set out to improve the breadth and depth of standardized data collection and analytical products ensure its products are widely used and recognized as the authoritative source for long-term population change information for most birds and secure adequate resources, internally and through partnerships, to realize the expanded vision of the BBS intended to support avian management needs through 2030.

The BBS Action Plan - A companion document to the Strategic Plan for the North American Breeding Bird Survey: 2020-2030, the BBS Action Plan identifies 28 specific actions for the U.S. Geological Survey, Canadian Wildlife Service, Mexican National Commission for the Knowledge and Use of Biodiversity and other possible collaborators providing a road map and starting points for accomplishing the three goals and eight strategic objectives of the BBS Strategic Plan over the next decade. The action plan is a living document, subject to annual review and updates as tasks are accomplished and priorities change through time.

Evening Grosbeak with BBS Trend Map (Credit: Mikey Lutmerding, USGS Patuxent Wildlife Research Center. Public domain.)

BBS Analysis - The North American Breeding Bird Survey (BBS) Summary and Analysis Website provides summary information on population change for >500 species of North American birds. The BBS provides data from 1966 for the contiguous United States and southern Canada (the “core” area), and the scope of inference expanded in 1993 to include additional regions in northern Canada and Alaska (the “expanded” area). The website provides geographic displays and quantitative information on population trend (interval-specific yearly percentage changes) and annual indices of abundance for each species at several geographic scales, including survey-wide, states and Provinces, Bird Conservation Regions (physiographic strata), and for individual survey routes in the United States. Custom analyses of population change allow of analysis of change for any combination of years over which the survey was conducted.

BBS Bird ID - The Bird Identification Infocenter is a collection of breeding and wintering distribution maps derived from North American Breeding Bird Survey and Christmas Bird Count data. Along with maps, images, song and call recordings, and life history information are provided for species encountered along BBS and CBC surveys.

Patuxent Bird Quiz - The Bird Identification Quiz was developed to allow users to test themselves on visual and aural identification of birds likely to be seen on North American Breeding Bird Surveys and Christmas Bird Counts. We also include a quiz in which users get to test their knowledge of wintering and breeding distributions of North American Birds.

Characteristics of Birds

Birds are endothermic, and because they fly, they require large amounts of energy, necessitating a high metabolic rate. Like mammals, which are also endothermic, birds have an insulating covering that keeps heat in the body: feathers. Specialized feathers called down feathers are especially insulating, trapping air in spaces between each feather to decrease the rate of heat loss. Certain parts of a bird’s body are covered in down feathers, and the base of other feathers have a downy portion, whereas newly hatched birds are covered in down.

Figure 1. Primary feathers are located at the wing tip and provide thrust secondary feathers are located close to the body and provide lift.

Feathers not only act as insulation but also allow for flight, enabling the lift and thrust necessary to become airborne. The feathers on a wing are flexible, so the collective feathers move and separate as air moves through them, reducing the drag on the wing. Flight feathers are asymmetrical, which affects airflow over them and provides some of the lifting and thrusting force required for flight (Figure 1). Two types of flight feathers are found on the wings, primary feathers and secondary feathers. Primary feathers are located at the tip of the wing and provide thrust. Secondary feathers are located closer to the body, attach to the forearm portion of the wing and provide lift. Contour feathers are the feathers found on the body, and they help reduce drag produced by wind resistance during flight. They create a smooth, aerodynamic surface so that air moves smoothly over the bird’s body, allowing for efficient flight.

Flapping of the entire wing occurs primarily through the actions of the chest muscles, the pectoralis and the supracoracoideus. These muscles are highly developed in birds and account for a higher percentage of body mass than in most mammals. These attach to a blade-shaped keel, like that of a boat, located on the sternum. The sternum of birds is larger than that of other vertebrates, which accommodates the large muscles required to generate enough upward force to generate lift with the flapping of the wings. Another skeletal modification found in most birds is the fusion of the two clavicles (collarbones), forming the furcula or wishbone. The furcula is flexible enough to bend and provide support to the shoulder girdle during flapping.

An important requirement of flight is a low body weight. As body weight increases, the muscle output required for flying increases. The largest living bird is the ostrich, and while it is much smaller than the largest mammals, it is flightless. For birds that do fly, reduction in body weight makes flight easier. Several modifications are found in birds to reduce body weight, including pneumatization of bones. Pneumatic bones are bones that are hollow, rather than filled with tissue (Figure 2). They contain air spaces that are sometimes connected to air sacs, and they have struts of bone to provide structural reinforcement. Pneumatic bones are not found in all birds, and they are more extensive in large birds than in small birds. Not all bones of the skeleton are pneumatic, although the skulls of almost all birds are.

Figure 2. Many birds have hollow, pneumatic bones, which make flight easier.

Other modifications that reduce weight include the lack of a urinary bladder. Birds possess a cloaca, a structure that allows water to be reabsorbed from waste back into the bloodstream. Uric acid is not expelled as a liquid but is concentrated into urate salts, which are expelled along with fecal matter. In this way, water is not held in the urinary bladder, which would increase body weight. Most bird species only possess one ovary rather than two, further reducing body mass.

The air sacs that extend into bones to form pneumatic bones also join with the lungs and function in respiration. Unlike mammalian lungs in which air flows in two directions, as it is breathed in and out, airflow through bird lungs travels in one direction (Figure 3). Air sacs allow for this unidirectional airflow, which also creates a cross-current exchange system with the blood. In a cross-current or counter-current system, the air flows in one direction and the blood flows in the opposite direction, creating a very efficient means of gas exchange.

Figure 3. Avian respiration is an efficient system of gas exchange with air flowing unidirectionally. During inhalation, air passes from the trachea into posterior air sacs, then through the lungs to anterior air sacs. The air sacs are connected to the hollow interior of bones. During exhalation, air from air sacs passes into the lungs and out the trachea. (credit: modification of work by L. Shyamal)


Why Study Birds?

Learn about the historical, cultural, and ecological reasons why birds are interesting and important subjects of study.

Avian Diversity and Classification

Discover how important avian taxonomy is to ornithological research and the potential pitfalls in the misclassification of birds.

Evolution and Speciation

Learn about the origin and speciation of birds, and their evolution into the diversity of species we see today.

Morphology: Feathers, Plumage and Flight

Talk by Ashwin Viswanathan

Delve into the details of complex feather structures, plumage pigmentation, and the dynamics of avian flight with an in-depth look at a bird’s external morphology.

Avian Anatomy and Physiology

Find out about the intricacies of birds’ skeletons, beaks, wings – along with the physiological functions that help them survive in a variety of habitats and occupy different niches.

Life Histories

Learn about the life history strategies that birds have to survive and reproduce.

Foraging Behaviour

Learn about how birds feed, what strategies they use to acquire food, and what interactions exist between their foraging behaviour and the environment they occupy.

Mating and Breeding Behaviour

Birds have some of the most fascinating, complex, and varied mating systems among vertebrates – learn about them, and how they evolved.

Social and Vocal Behaviour

Birds don’t use only songs or calls exclusively – find out how they have adapted various processes to use acoustics to their benefit in their social structures for a range of needs.


Talk by Ashwin Viswanathan

Learn about why and how birds migrate, the challenges they face in an ever-changing world.

Bird Populations

Understand bird population densities, survival and trends along with the basics of the mathematical models used to understand patterns and processes underlying population dynamics.

Bird Communities

Learn about how bird communities are formed, how niches are filled, and how birds of different guilds are vital in fulfilling the ecological roles in an ecosystem.


Learn about the role geography plays in determining how far species can disperse and how it influences species diversity at a location.


Learn about the environmental factors that influence the abundance and distribution of birds at large spatial scales.

Bird Conservation

Talk by Umesh Srinivasan & Mousumi Ghosh

An introduction to bird conservation using South Asian vulture declines as a case study.


Why Study Birds?

Learn about the historical, cultural, and ecological reasons why birds are interesting and important subjects of study.

Avian Diversity and Classification

Discover how important avian taxonomy is to ornithological research and the potential pitfalls in the misclassification of birds.

Evolution and Speciation

Learn about the origin and speciation of birds, and their evolution into the diversity of species we see today.

Morphology: Feathers, Plumage and Flight

Talk by Ashwin Viswanathan

Delve into the details of complex feather structures, plumage pigmentation, and the dynamics of avian flight with an in-depth look at a bird’s external morphology.

Avian Anatomy and Physiology

Find out about the intricacies of birds’ skeletons, beaks, wings – along with the physiological functions that help them survive in a variety of habitats and occupy different niches.

Life Histories

Learn about the life history strategies that birds have to survive and reproduce.

Foraging Behaviour

Learn about how birds feed, what strategies they use to acquire food, and what interactions exist between their foraging behaviour and the environment they occupy.

Mating and Breeding Behaviour

Birds have some of the most fascinating, complex, and varied mating systems among vertebrates – learn about them, and how they evolved.

Social and Vocal Behaviour

Birds don’t use only songs or calls exclusively – find out how they have adapted various processes to use acoustics to their benefit in their social structures for a range of needs.


Talk by Ashwin Viswanathan

Learn about why and how birds migrate, the challenges they face in an ever-changing world.

Bird Populations

Understand bird population densities, survival and trends along with the basics of the mathematical models used to understand patterns and processes underlying population dynamics.

Bird Communities

Learn about how bird communities are formed, how niches are filled, and how birds of different guilds are vital in fulfilling the ecological roles in an ecosystem.


Learn about the role geography plays in determining how far species can disperse and how it influences species diversity at a location.


Learn about the environmental factors that influence the abundance and distribution of birds at large spatial scales.

Bird Conservation

Talk by Umesh Srinivasan & Mousumi Ghosh

An introduction to bird conservation using South Asian vulture declines as a case study.

Watch the video: BIRDS Names and Sounds - Learn Bird Species in English (July 2022).


  1. Ugutz

    Drain, And how !!!

  2. Westleah

    This is the precious coin

  3. Humphrey

    Remarkable, useful thought

  4. Ungus

    There is something in this. Thank you so much for your help in this matter, now I will not make such a mistake.

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